The invention relates to magnetic transducers for reading information signals from a magnetic medium. In particular, the invention relates to an improved method of depositing magnetoresistive heads which include a layer of antiferromagnetic material suitable for exchange stabilization of the magnetoresistive sensor.
Magnetoresistive (MR) heads with magnetoresistive elements (MREs) or sensors are known magnetic transducers which are capable of reading data from the surface of a magnetic media at higher densities than inductive sensor heads. MR sensors detect flux changes in a magnetic media as resistance changes in the sensor. The MR sensor is made from a ferromagnetic magnetoresistive material which exhibits resistance changes as a function of the amount and direction of magnetic flux being sensed by the element.
Permalloy (with a composition near 80 Ni 20 Fe, but abbreviated as NiFe) is frequently used as material for MR sensors because of its high magnetic permeability and good magnetoresistive response (known as .DELTA.p). When an NiFe MR sensor is exposed to external magnetic fields, it can be transformed from a single-domain sensor into multi-domain sensor. Transformation of the NiFe MR sensor from single domain into multi-domain is undesirable because of the resulting lack of stability and loss of output amplitude from the sensor.
One method Of maintaining NiFe MR sensors in a single domain state is known as exchange field stabilization. Exchange field stabilization of MR heads involves the use of an anti-ferromagnetic thin film material, such as 50 Fe 50 Mn, to stabilize the NiFe MR sensor. A great deal of research has been done on the use of materials such as FeMn to stabilize NiFe MR sensors. In exchange field stabilization, one of the magnetic lattices of the antiferromagnetic film couples to the magnetic lattice of the NiFe film. Since the FeMn film is not susceptible to stray fields, this coupling between the antiferromagnetic film and the NiFe film preserves the domain state of the MR sensor from the influence of the stray field.
Prior research and publications in the art concerning the use of FeMn to achieve high exchange coupling for exchange stabilization of MR heads have disclosed methods of producing MR heads which present a number of manufacturing difficulties. For instance, the prior art publications report that after depositing the NiFe and FeMn films, the films must be annealed at temperatures as high as 270.degree. C. for time periods as long as several days in order to achieve high exchange fields. Annealing at these high temperatures and for these extended periods of time is not practical for manufacturing large quantities of MR heads. Many of these prior art methods require multiple anneal cycles which is time consuming and undesirable in a manufacturing environment. Also, known fabrication techniques use power densities as high as 2.6 W/cm.sup.2 to sputter deposit the films, which can cause substantial interdiffusion of the films at their interface. Additionally, in order to create an NiFe MR sensor with the proper magnetic domain orientation, prior art manufacturing methods normally require that the NiFe film be sputter deposited in the presence of an applied external magnetic field using permanent magnets attached to the pallet near the wafer. However, if the FeMn film is sequentially sputter deposited without breaking vacuum, the external applied magnetic field makes it difficult to maintain thickness uniformities of more than .+-.10 percent which, in some MR head designs, is critical.
One attempt to improve the manufacturability of MR heads while maintaining adequate exchange fields is disclosed in U.S. Pat. No. 5,262,914 which issued Nov. 16, 1993 to Chen et al. Chen et al. discloses a method of producing an MR sensor with a claimed reduction of innealing temperatures and times to 240.degree. C. and seven hours, respectively. However, the method of producing MR heads with enhanced exchange field of Chen et al. requires the addition of a thin layer of interdiffusion material such as Au in contact with the layer of FeMn. This addition of an extra thin film layer causes an undesirable increase in manufacturing complexity, as well as other design related problems. For instance, many MR head designs use Au, for example, as contacts for the MR head. In Chen et al., in order to allow the Au to diffuse into the FeMn, films such as Ta and Mo which act as adhesion promoters and diffusion barriers must be removed. Requiring diffusion of Au into FeMn, while preventing it from entering NiFe, increases manufacturing complexity. Also, in most MR head designs, the layer or layers of Fe Mn are kept as thin as possible in order to reduce the height of the device. Frequently, the layer of FeMn will be around 150 Angstroms. With such a thin layer of FeMn, the Au or other interdiffusion material is capable of diffusing through the layer of FeMn and into the NiFe sensor, possibly adversely affecting the NiFe sensor's performance.